Downhole power dissipator

ABSTRACT

A downhole power dissipator for protecting a packer in a casing in a well bore from a sudden increase in pressure by providing a closed collapsible chamber positioned adjacent the packer and preferably between the packer and the point of pressure increase. Said chamber includes a compressible gas and means allowing the gas in the chamber to become compressed when the chamber is subjected to a predetermined external increase in pressure. The chamber is attached to the packer whereby the chamber is retrievable from the well bore and said chamber including a passageway for passage of well equipment.

United States Patent 1191 Kilgore 1 Jan. 9, 1973 Marion D. Kilgore, Houston, Tex.

521 u.s.c1 ..166/243,166/242 51 Int.C1. ..E21b43/00 58 Field in Search ....175/4.54; 166/55.l, 107, 163,

[56] References Cited UNITED STATES PATENTS 2,812,717 11/1957 Brown ..l66/243 3,311,178 3/1967 McElheny ..175/4.54

Primary Examiner-David H. Brown Attorney-James F. Weiler, Jefferson D. Giller, William A. Stout, Paul L. DeVerter, 11, Dudley R. Dobie,

Jr. and Henry W. Hope [57] ABSTRACT A downhole power dissipator for protecting a packer in a casing in a well bore from a sudden increase in pressure by providing a closed collapsible chamber positioned adjacent the packer and preferably between the packer and the point of pressure increase. Said chamber includes a compressible gas and means .allowing the gas in the chamber to become cornpressed when the chamber is subjected to a predetermined external increase in pressure. The chamber is attached to the packer whereby the chamber is retrievable from the well bore and said chamber including a passageway for passage of well equipment.

8 Claims, 5 Drawing Figures PATENTEDJAN 91975 3.709 .294

sum 2 or 2 ATTORNEY-I INVENTOR. I

DOWNHOLE POWER DISSIPATOR BACKGROUND OF THE INVENTION There are circumstances that arise in the well bore, particularly in an oil and gas well, that create pressure and shock surges that are potentially damaging to well bore equipment, such as tubing, casing, packers and other downhole well equipment. For example, sudden pressure surges and shock waves are created when perforating a casing adjacent a packer. In fact, in the past, many packers and/or casings have been ruptured by the high pressures and shock waves created when perforating, particularly when the tubing or casing contains incompressible fluids such as water and/or mud. The present invention is directed to an apparatus which re lieves the pressure increase thereby protecting the downhole well equipment and yet does not interfere with well operations.

SUMMARY point of pressure increase with the chamber including a compressible gas and having means for allowing the gas in the chamber to become compressed when the chamber is subjected to a predetermined increase in external pressure thereby relieving and absorbing the pressure increase and protecting the downhole well equipment from the pressure and shock waves created by the sudden pressure increase.

A further object is the provision of a downhole power dissipator which is attached to the packer and which may thus be-retrieved after serving its purpose and avoids leaving undesirable debris in the well.

Another object of the present invention is the provision of a downhole power dissipator which may repeatedly absorb pressure increases and shock waves in a well bore by providing compressible gas in the dissipator.

Still a further object of the present invention is the provision of a downhole power dissipator which has a passageway forthe passage'of well tools therethrough and wherein the gas in the closed chamber is at a pressure lower than the normal pressure in the well to-provide an increased fluid volume for relieving and absorbing any sudden pressure increase.

Still a further object of the present invention'is the provision of frangible means in the chamber for opening the chamber when subjected to a sudden increase in external pressure.

Yet a further object is the provision of piston means for collapsing the chamber for allowing gas in the chamber to be compressed when the chamber is subjected to an external predetermined higher pressure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view, partly schematic, illustrating one embodiment of the present invention in position in a well bore adjacent a well packer,

FIG. 2 is an enlarged cross-sectional view of another embodiment of the collapsible chamber of the present invention, I

FIG. 3 is an enlarged cross-sectional view of the collapsible chamber of the present invention with still a further means for allowing the gas therein to be compressed,

FIG. 4 is an enlarged cross-sectional view of another embodiment of the present invention, and

FIG. 5 is an enlarged cross-sectional view of still a further embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and particularly to FIG. 1, a well bore 10 'is shown having a casing l2 therein and a well tubing 14 and a packer 16 forming a seal between the well tubing 14 and casing 12, all as is conventional.

As previously mentioned, there are occasions when sudden pressure surges occur in a well bore which damage the casing 12, tubing 14, packer l6 and other downhole well equipment. By way of example only, a gun perforator 18 is shown positioned below thepacker 16 for perforatingthe casing 12. That is, the gun l8 creates perforations in the casing 12 by firing projectilesthro ugh the wall of the casing 12 which creates sudden pressures and shock waves which have at many times in the past ruptured the casing l2,the packer l6 and other downhole equipment. This problem can become more severe in those cases where the casing 12 and tubing 14 include a non-compressible fluid such as water or mud. For example .only, while the downhole pressure may be 4000 psi, the momentary surge pressure caused by perforating mayv be as great as 20,000 psi. Obviously, when incompressible fluids or even gases are exposed to such increased pressures, severe damage may be caused to the downhole equipment particularly in an environment where a packer confines the force of the explosion to a small area.

The present invention is directed to providing a collapsible chamber generally indicated by the reference numeral 20 which has the effect of increasing the fluid volume in the well bore for relieving and absorbing any sudden pressure increase. The chamber 20 of the present invention is a closed but collapsible chamber which is positioned preferably between the packer 16' and the point of pressure increase thereby protecting the packer 16 from the sudden pressure surge such as occasioned by the perforating gun"l'8. The chamber 20 includes a compressible gas to insure that at least a porexternal pressure. One type of such means is shown in FIG. 1 as an enclosed thin wall container, for example thin metal, having a predetermined collapsing strength, depending upon the pressure, surge to be protected against, and which will buckle or crumble and collapse upon the application of external pressure thereby absorbing and relieving any shock or pressure increase. Preferably, the chamber is attached or connected to the packer 16, such as by threads 21, and may be retrieved from the well bore when the packer 16 is retrieved thereby avoiding the problem of leaving debris or remnants of the collapsed chamber 20 in the well bore which may interfere with other well operations or otherwisecause an unnecessary fishing operation. And while the collapsible chamber 20 is shown in FIG. 1 as being below the packer 16, the chamber may be placed in any position desired above or below the packer 16. In addition the chamber 20 may include an opening 23 therethrough which allows the passage of conventional well equipment. Referring now to FIG. 2, a closed collapsible chamber member 26 is provided adapted to be connected to a packer or well tubing by means of threads 28 and/or 30 and includes a rigid body 30 with a ring shapedopening member 32 sealing the chamber from theexterior by seal means 34 and normally is held in place by frangible means such as shear pins 36. Thus, when the exterior pressure overcomes the shear pins 36 the opening member 32 is moved inwardlyexposing the compressible gas in the chamber 26 for providing an'increase in the well bore fluid volume. The body 30 includesalip 33 for retaining the member and preventing it from dropping into the well after the pins 32 are sheared.

FIG. 3 isa cl'osedcollapsible chamber 38 having a body 40 which is held closed by a piston 42 having a seal means 44. A spring 46 may be provided which acts against the piston 42 in a direction to keep the piston from normally compressing the gas in the chamber 38. When a predetermined external pressure acts against the piston 42, the piston 42 is pressed against the spring 46 overcoming the spring and the pressure of the gas in the chamber 38 to .act to absorb the pressure increase in the well borefThe embodiment of FIG. 3 also includes suitable and conventional threads 48 and 50-for suitablyconnecting the chamber above or below the packer .16. However, the spring 46 in FIG. 3'may be omitted, and the pressure in the chamber 38 may be selected equal to or greater than the normal bottom hole pressureinthe casing 12 to act against the piston 42. For example only, assume the following well conditions:,6,000 feet deep, packer l6 landed and set, tubing 12 full of salt water, and bottom hole'pressure in vicinity of packer is 3,000 psi. Prior to running-the installation, the chamber 38 could have been chargedwith can be designed suchthat thepressure increase in the chamber can be held at safe levels, while stillproviding ample relief for thepressure surge. 7

However, the embodiment shown in' FIG. 3 utilizes moving seals 44 which is subject to deterioration and possibly leaking. The embodiment of FIG. 4 utilizes a chamber 52 enclosed by a flexible bellows 54, such as metal, which is charged with gas through valve 56, and will contract and expand as required to provide a power dissipator which can repeatedly be used without withdrawing it from the well bore. A stop 58 is p'ro'-- case, it would be preferable that the .internal pressuretherein would be equal to or greater than the bottom hole pressure.

Yet, a still further embodiment is shown in FIG. 5

wherein the chamber includes a plurality of hollow containers which are retained in place in the body 62 by a-retaining disc 64. The containers may be hollow glass balls which will break upon a predetermined external pressure, or thecontainers may be resilient, such as rubber, so as to provide a power dissipator which may be repeatedly used in the Well bore In use, the closed collapsible chamber of the present invention is placed in the vicinity of, such as connected to, the packer 16 to protect'the downhole well equip: ment if and when a potentially'dangerous and damaging pressure or shock wave is encountered. In such event,- the chamber will provide achange in the well bore fluid volume such that the pressure surge or shock wave is cushioned and dissipated. Preferably, the chamber is connected, to the packer, either above or. below, so that it can be retrieved after use without leaving undesired debris in the wellbore. In addition, the chamber is preferably positioned between the packer and point of the pressure increase to provide maximum protection for the packer. I

The-present invention, therefore,"iswell adapted to carry out the objects and attain the ends and advantages mentioned as well as othersinherent therein.

, What is claimed is:' 4

l. A downhole power. dissipator for protectinga packer in a well bore'from a suddeni'ncrea'se in pressure comprising, v

a closed collapsible chamber positioned adjacent the packer! I said chamber including a compressible gas, and

- said chamber including frangible means foropening said chamber allowing the gas in the chamber to become compressed when the chamber is subjectedto a predetermined increase in external pressure. j v 2. A downhole power dissipator for protecting a packer in a well bore froma sudden increasein pres 3. A downhole power dissipator for protecting a.

in pres-- packer in a well bore from a sudden increase sure comprising,

a closed collapsible chamber positioned adjacent the packer,

said chamber including a compressible gas, and

said chamber including means allowing the gas in the chamber to become compressed when the chamber is subjected to a predetermined increase in external pressure, said chamber including a plurality of hollow sealed containers which are collapsible and exposed to pressure in the well bore when the dissipator is positioned therein.

4. A downhole power dissipator for protecting a packer in a well bore from a sudden increase in pressure comprising,

a closed collapsible chamber positioned adjacent the packer, said chamber including a compressible gas, and

said chamber including means allowing the gas in the chamber to become compressed when the chamber is subjected to a predetermined increase in external pressure, said chamber including a passageway therethrough for the passage of well equipment.

5. A downhole power dissipator for protecting a packer in a casing in a well bore from a sudden increase in pressure comprising,

ing the gas to become compressed includes a piston.

7. The apparatus of claim 6 including,

a spring acting against the piston in a direction keeping the piston from compressing the gas. 8. The apparatus of claim 6 wherein the gas in the chamber acts against the piston and is at a pressure at least as great as the normal pressure in the well bore but is of a pressure less than the surge pressure encountered in the well bore. 

1. A downhole power dissipator for protecting a packer in a well bore from a sudden increase in pressure comprising, a closed collapsible chamber positioned adjacent the packer, said chamber including a compressible gas, and said chamber including frangible means for opening said chamber allowing the gas in the chamber to become compressed when the chamber is subjected to a predetermined increase in external pressure.
 2. A downhole power dissipator for protecting a packer in a well bore from a sudden increase in pressure comprising, a closed collapsible chamber positioned adjacent the packer, said chamber including a compressible gas, and said chamber being enclosed by a wall which collapses when the chamber is subject to a predetermined external pressure, thereby allowing the gas in the chamber to become compressed.
 3. A downhole power dissipator for protecting a packer in a well bore from a sudden increase in pressure comprising, a closed collapsible chamber positioned adjacent the packer, said chamber including a compressible gas, and said chamber including means allowing the gas in the chamber to become compressed when the chamber is subjected to a predetermined increase in external pressure, said chamber including a plurality of hollow sealed containers which are collapsible and exposed to pressure in the well bore when the dissipator is positioned therein.
 4. A downhole power dissipator for protecting a packer in a well bore from a sudden increase in pressure comprising, a closed collapsible chamber positioned adjacent the packer, said chamber including a compressible gas, and said chamber including means allowing the gas in the chamber to become compressed when the chamber is subjected to a predetermined increase in external pressure, said chamber including a passageway therethrough for the passage of well equipment.
 5. A downhole power dissipator for protecting a packer in a casing in a well bore from a sudden increase in pressure comprising, a closed collapsible chamber connected to the packer and positioned between the packer and the point of pressure increase, said chamber including a compressible gas, said chamber including means allowing the gas in the chamber to become compressed when the chamber is subjected to a predetermined increase in pressure external to the chamber, and said chamber including an opening therethrough for the passage of well equipment.
 6. The apparatus of claim 5 wherein the means allowing the gas to become compressed includes a piston.
 7. The apparatus of claim 6 including, a spring acting against the piston in a direction keeping the piston from compressing the gas.
 8. The apparatus of claim 6 wherein the gas in the chamber acts against the piston and is at a pressure at least as great as the normal pressure in the well bore but is of a pressure less than the surge pressure encountered in the well bore. 